Human genes reflect impact of historical events

BERLIN (AP) — Tell-tale relics of Europe's colonial period, the Mongol empire and the Arab slave trade can be found in the genes of modern humans, scientists said Thursday.

Researchers from Britain and Germany used almost 1,500 DNA samples from 95 different populations across the world to produce a map showing genetic links stretching back 4,000 years. By examining the moment when a particular part of DNA first appears, they were able to tie the genetic mixing of populations to historical events.

Some of these links have long been assumed, but others came as a surprise, said Daniel Falush, a researcher at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who co-authored the paper published in the journal Science.

DNA samples from the Tu people of China indicate they mixed with a European group — related to modern Greeks — around A.D. 1200. One likely possibility is the European DNA came from traders traveling the Silk Road.

Another interesting find seems to bolster the legend among the Kalash people of Pakistan they are descendants of Alexander the Great's army, Falush said.

Samples show that the Kalash were genetically isolated for a long period going back to about B.C. 300 — around the time of Alexander's military campaign in Asia.

"Our dating fits very well with their legend," Falush said.

Using a technique called "chromosome painting," the researchers were also able to illustrate the genetic flow caused by other historical events, such as the Arab slave trade that introduced African DNA to populations around the Mediterranean, the Arab Peninsula and what is now Iran and Pakistan from A.D. 800-1000.

The results help scientists to pin-point the population effects of such historical events, said Graham Coop, an associate professor of population genetics at the University of California, Davis.

"We have historical records of some of these events, but rarely do we know the demographic impact of such events," said Coop, who wasn't involved in the research.

Similar studies may become harder to perform in the future, as population mixing speeds up because of global migration, Falush said.

"We hope this will encourage people to collect samples soon," he said.